Conventional I.S. glassware forming machines form glass bottles by what is known in the art as either a "press and blow" or a "blow/blow" method. Gobs of molten glass are delivered first to a parison or blank mold station where molten glass gobs are preformed into hollow parisons or blanks by either a pressing or blowing operation. Thereafter, the parisons are transferred to a blow mold station by an inverting movement which carries the parisons through a 180.degree. arc to open pairs of blow mold halves which then close about the parisons. The parisons are then blown in a fashion which permits them to assume their final form inside the blow molds. At each station, the mold halves are opened and closed by mold holder arms secured to rotatable shafts.
It is important that the mold holder arms open and close properly in order that the forming operations at the blank and blow mold stations are properly performed. Various mechanisms have been employed for this purpose. One approach to the design of such mechanisms, favored for its simplicity and reliability, has been to employ a fluid actuated piston and cylinder to simultaneously move the mold holder arms between their open and closed positions. A mold opening and closing mechanism of this type is disclosed in U.S. Pat. No. 2,702,444 to Rowe. In the Rowe device, the molds are open and closed by pneumatic actuation of a single piston having a double ended piston rod, the ends of which have gear racks which mesh with segment gear arms. The gear arms are connected by separate linkages to shafts which actuate the mold holder arms. A disadvantage of mechanisms of this type is that even a slight amount of drag or misalignment anywhere in the linkage system or within the piston chamber can translate and be magnified through the linkages to the mold halves, resulting in eccentric movement of the mold halves. If the mold halves are off center by as much as ten- to fifteen-thousandths of an inch, seams in the glass product and other unacceptable problems will result.
A dual rack with a common pinion gear is disclosed in U.S. Pat. No. 3,445,218. The mechanism disclosed therein uses a single piston design with a gear rack and sector gear to drive the pinion gear. The pinion gear in turn drives the racks which open and close the mold halves. Serial transmission of the piston-actuated opening and closing force through a series of gears can result in mechanical inefficiency and increased wear and breakdown.
What is needed is a hydraulic mold opening and closing mechanism which provides improved security against misalignment of the mold halves.